1. Field of the Invention
The present invention relates to carbon black pellets and, more particularly, to carbon black pellets having good dispersibility, good bulk handling characteristics and good attrition resistance, and to a method of manufacturing such pellets.
2. Description of Prior Art
Carbon black finds wide industrial use. Carbon black is used as a reinforcing agent in rubber products such as tires, tubes, conveyor belts, cables and other mechanical rubber goods; as a black pigment in printing, lithographic, letter press, carbon paper and typewriter ribbon inks, paints, coatings, lacquers, plastics, fibers, ceramics, enamels, paper, record discs and photocopier toner; in leather finishes; in the manufacture of dry-cell batteries, electrodes and carbon brushes; in electrical conductors; in conductive and anti-static rubber and plastic products; for electromagnetic interference shielding; video discs and tapes; for UV stabilization of polyolefins; as a high temperature insulating material; etc.
As produced, carbon black particles have a fractal morphology. They are composed of primary particles about 10 to 500 nm in diameter which irreversibly fuse during the furnace/combustion process used and produce primary aggregates having a diameter of from 50 to 20,000 nm. Carbon black cannot be practically used in its produced form because of its light and dusty form making its handling, shipment and end use not only difficult but environmentally unacceptable. To improve these handling, shipping and use problems, the produced, fluffy carbon black is densified. It is well known in the art that for a given grade of carbon black, handling properties improve with increasing degree of densification. However, dispersibility of the densified carbon black is progressively degraded as the extent of densification is increased. Thus, there is a trade off between improvements in bulk handling properties and degradation in dispersibility.
In general, currently the industry uses three basic methods to obtain densification. These, in order of providing increased levels of densification are: agitation or vacuum treatment of the fluffy produced product, dry pelletization and wet pelletization. All of these methods are well documented in the art as disclosed, for example, in U.S. Pat. Nos. 2,850,403; 3,011,902; 4,569,834; 5,168,012; 5,589,531; and 5,654,357, all of which are incorporated herein by reference for all purposes. The densification processes mentioned above, all suffer from disadvantages, e.g., product that has poor properties in bulk handling, the formation of pellets which are relatively weak and have poor attrition resistance or relatively dense, hard and attrition resistant pellets which possess good bulk handling properties but are difficult to disperse.
Thus there still remains a need for a densified carbon black which exhibits good bulk handling properties, has good attrition resistance and is readily dispersible.